The present invention relates to optocouplers and more particularly to an optocoupler which can isolate a low voltage section of a circuit from a high voltage section wherein the input current signal is converted linearly to an output current.
Conventional optocouplers typically isolate voltages of only about 10,000 volts or less. In such devices, the light emitting mechanism is closely spaced from the detector with a clear dielectric material provided between the emitter and detector for transmission of light. Because the emitter and detector are closely spaced, loss of light transmission is less of a concern to the efficiency of the transfer. However, where high voltage isolation is concerned, the emitter and detector must be spaced relatively far apart from each other to avoid arcing. Because the emitter and detector are spaced far apart and because the magnitude of the signal generated by the detector is relatively small, e.g. on the order of millamps, it is difficult in conventional mechanisms to achieve a high current transfer ratio (without amplification) due to loss of light transmission and non-linear conversion of the input current to an output current.
Prior attempts to provide high voltage isolation optocouplers have not been able to achieve highly efficient light transmission or high current transfer ratio (ratio of output current to input current) without costly and complex optical transmission design features. In order to reduce cost, conventional high gain photodetectors have been employed which do not necessarily provide a linear detection response and exhibit gain drift with variation in temperature.